When the British filmmaker Danny Boyle went to Mumbai, India, to make a movie, he found what has all but vanished from cinema here at home: life in extremis.

He also lost what he once considered central to his craft — the power to control what unfolds in front of his camera.

In Mumbai, which is also known as Bombay, thousands of people gathered every time he started shooting “Slumdog Millionaire” on the streets. Permits were delayed, then granted in the nick of time. Sometimes the city morphed overnight, as new construction sites came up and down. Best-laid plans proved useless. India took over. Kindly adjust, it seemed to say. “You have to let go,” is how Mr. Boyle described the experience this month, in an interview on tamed, temperate Long Acre here. “You don’t act omnipotent. You have to let whatever is there get into the film.”

The result is a part-vérité, part-magical journey into ground zero of the Indian dream — a Mumbai slum — with a film that tells the story of love, pluck and greed through the eyes of a child forced to grow up too soon.

“Slumdog Millionaire” is ostensibly about a young contestant on the Indian version of “Who Wants to Be a Millionaire.” The story of his short but rich life unfolds in a series of flashbacks, one game-show question at a time. Foreign audiences will find some of those flashbacks to be brutal, even revolting, but such is an Indian slum dog’s life. And Mr. Boyle, 52, the maker of films as varied as “Trainspotting,” “The Beach” and “28 Days Later,” does not flinch from it. He sees this as a movie about memory, each remembrance pulling the hero closer to the woman of his dreams.

The movie opened in the United States on Wednesday, and is to be released in India in late January, assuming it can clear that country’s often-prickly censor board.

Perhaps the most remarkable thing about “Slumdog Millionaire” is that, despite the director’s strenuous denials, it could well be a Bollywood film, “almost an homage to the ’70s masala potboiler” of Indian cinema, the film’s co-director, Loveleen Tandan, called it. Its protagonist is an underdog striving to strike gold, flanked by a malevolent brother and an underworld don, with a woman stuck in the middle — all classic elements of popular Indian cinema.

The movie is awash with song — and even a little dance. There is a proper Bollywood star, the fabulously creepy Anil Kapoor with his fabulously creepy slicked-back hair. Most audaciously, for a film that expects to win over an American audience, close to a third of the dialogue is in Hindi, with English subtitles. Imagine Abbas Kiarostami making a Western, with a third of the dialogue in English.

The decision to go with Hindi stemmed from a need to find child actors who could be true to the characters in the script. Ms. Tandan, who is Indian, said it was impossible to find English-speaking Indian children who could play hard-knuckles slum kids. Mr. Boyle immediately understood that, she said, and agreed to rewrite the script into Hindi. Ms. Tandan ended up hiring real kids, some of them from the Mumbai slums, to play the three lead child characters.

“For us it’s almost like a validation of our celebration of cinema, the way we tell our stories,” Ms. Tandan said. “It feels like it’s ours.”

“Slumdog” is decidedly not Bollywood in one crucial respect: It was shot on the streets of Mumbai, from the dense warrens of a tin-roofed shantytown to a red-light district to the architectural landmark Victoria Terminus train station. Most Bollywood filmmakers do not shoot on the streets of the city — they recreate it in studios or they choose to shoot in more exotic locales (Brooklyn, for instance) — because that way, as the “Slumdog” crew learned, lies a certain madness. Mumbai is not only crowded, it is also a city where tens of thousands of people live on the streets. The street is their living room; why wouldn’t they crowd around Mr. Boyle’s crew?

Christian Colson, the producer, recalled that during filming in the red-light alley at least 3,000 people encircled the crew. They didn’t all seem friendly. To try to drive away the crowds would be folly, Mr. Boyle quickly realized; not only would the effort be costly, but a new one would gather just as fast. Sometimes, he recalled, he would leave a scene not quite knowing whether he had gotten the shot he needed. Invariably it turned out that he had much more.

“The control freak would say you need a bigger army,” he said. “It’s not about that really. If you go with it, if you abandon that kind of control freakery, it will give you something extra.”

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There were many lessons in cross-cultural understanding. On scheduling, an Indian cast and crew simply didn’t operate in what Mr. Colson called the militaristic style of a British operation. There was the Indian bureaucracy: permits would arrive a few minutes before a scene was to be shot, or at least once, after it had been shot. And then there was the need for, well, a certain authenticity. On one occasion, Mr. Colson recalled, the Indian authorities took umbrage at a scene in the script in which a suspect is tortured by a police commissioner during interrogation. The Indian authorities told Mr. Colson to take out the police commissioner. No police officer above the rank of inspector should be shown administering torture, they said. The makers of “Slumdog Millionaire” obeyed.

For Mr. Boyle one of the toughest challenges was casting the lead role: the 18-year-old protagonist, Jamal Malik. He auditioned one young Indian actor after another. Many of them were capable, but they all looked buffed out, Mr. Boyle recalled, because they were all grooming for roles in Indian cinema.

In the end Mr. Boyle went with an actor his teenager daughter recommended: Dev Patel, from the British television series “Skins.” That choice could be called the most dissonant part of “Slumdog Millionaire.” Though he is a fine actor, Mr. Patel’s accent gives away who he is: a Briton of Indian origin. Not a kid from a Mumbai slum.

For Mr. Boyle the only knowledge he had of Mumbai came from the stories his father told. As a soldier in the British Army during World War II he had been stationed there, en route to Japan, “waiting to die,” as Mr. Boyle put it.

“He was there in Bombay when the bomb was dropped on Hiroshima,” he said. “He said, ‘We all knew we were going to go home.’ ”

Mr. Boyle’s Mumbai picture is based on a novel, “Q&A,” by the Indian writer Vikas Swarup, and adapted by Simon Beaufoy, the British screenwriter best known for his Oscar-winner, “The Full Monty.” Shot over three months, for about $13 million, “Slumdog Millionaire” was temporarily orphaned when its original backer, Warner Independent Pictures, was shut down this year. Stuck with the movie and facing a crowded release schedule of its own, Warner Brothers, the mini-studio’s corporate parent, contracted with Fox Searchlight to distribute and market the movie in North America. In September “Slumdog” won the People’s Choice Award at the Toronto International Film Festival.

Mr. Colson, the producer, said he likes to think of “Slumdog Millionaire” as a Dickensian story playing out in the Asian megalopolis of the future: “Oliver Twist set in Mumbai.”

Mr. Boyle, for his part, does not think he has made an Indian movie. “No, no, no, it’s not a Bollywood film. It’s a good story. It’s a narrative.”

But there is a reason it is set in Mumbai. “The extremes of storytelling are available there,” he explained, “and it’s kind of disappearing here.” There is also a reason the movie had to be shot there. Whatever you call it, Mumbai or Bombay is not a city that can be manufactured on a set, Mr. Boyle maintained. It is not distinguished by its architecture, but by its atmosphere, its noise. “Slumdog Millionaire” captures all of that, though because it is a movie, it misses one thing that truly distinguishes Mumbai, the way it smells: part drying fish, part human waste.

“You immediately know, don’t fake it,” Mr. Boyle said. “You feel a miasma of detail in a city. It is just marching. You are racing forward. You have to go with it.”

A version of this article appears in print on , on Page AR14 of the New York edition with the headline: Extreme Mumbai, Without Bollywood’s Filtered Lens. Order Reprints|Today's Paper|Subscribe